Vacuum tube filament supply



Sept. 24, 1940. J FNCH 2,215,521

' VA UUM TUBE FILAMENT SUPPLY Filed May 20, 1938 2 Sheets-Sheet lINVENTOR.

. JjgES L. F/NCH I 0 BY SEC. 360

ATTQRNEY.

Sept. 24, 1940.. J F|NH 2,215,521

VACUUM TUBE FILAMENT SUPPLY Filed May 20, 1958 2 Sheets-Sheet 2INVENTOR. JAM/4Z5 L. F/NCH A TTORNEY.

Patented Sept. 24, 1940 UNITED STATES VACUUM TUBE FILAME'NT'SUPPLY JamesLeslie Finch, Patchogue, N. Y., assignor to Radio Corporation ofAmerica, a corporation of Delaware Application May 20, 1938, Serial No.208,964

11 Claims. My invention relates to audio frequencyand radio frequencypower amplifiers in which 2.1--

ternating current is used to heat the filaments of the vacuum tubes. Inradio frequency power amplifier applications it relates particularly tothose services in which the modulation resulting from the A. C.filaments is objectionable such as in connection with telephone service.Polyphase filaments are already in use for the purpose of affecting areduction in the modulation due to V the A. C. filaments. My inventionresides in an improved method of using polyphase filaments for furtherreduction of this modulation.

In the prior art tubes having polyphase filaments composed of sixfilament wires, one end of each being connected to six external filamentterminals and the other end of each being connected to an internalneutral point are well known. Three phase filament power is used withthese tubes in which the filament wires are connected in pairs, eachpair forming one leg of a three phase star circuit. They are also usedwith six phase power, in which case each filament wire forms a leg of asix phase star circuit though this six phase connection results in nomaterial improvement over the three phase con-' nection. The reason forthis will be understood from the following analysis.

Modulation of the plate current and modulation of the amplified radiofrequency current by the A. C. filament current is largely due to themagnetron effect of the current. The filament current in each filamentwire sets up a magnetic field around it. This field tends to deflectelectrons leaving the filament and to impede their travel toward theplate. The higher the filament current the greater this effect becomes.This results in a modulation of the plate current and of the gain of theamplifier when alternating current is used in the filament. Thefrequency of this modulation is twice that of the filament currentbecause the efiect of the current is practically thesame regardless ofits direction. Thus for 60 cycle filament current the output/from theportion of the tube corresponding to each filament wire is modulated ata frequency of 120 cycles and at frequencies which are harmonics of 120cycles. When three phase, 60 cycle fila- 50 ment current is used theresulting 120 cycle modulation in each leg is displaced one-third of acycle from that of the other legs. This results very largely in acancellation of the 120 cycle and 240 cycle components and leaves the 55360 cycle. and higher frequency components inthe output as the only onesof any material consequence. When six phase filament current is used nomaterial improvement over three phase is obtained because with the sixphase connection there is no difference in the filament cur- 5 rentsexcept that the current in one of each of the pairs referred to above isin the opposite direction from that in the other wire of the pair. Thusthe modulation components of 360 cycles and its multiples are present inthe output in essentially the same way as when three phase power isused.

In my invention I connect the six filament terminals of the tubeheretofore described to a specially connected transformer whereby the360 cycle components of the modulation are also largely cancelledleaving only the 720 cycle components and multiples of 720 cycles.

A better understanding of the present invention will be had by referenceto the following detailed description, which is accompanied by drawingsin which,

Figure 1- is a circuit diagram of the primary and secondary of afilament transformer connected in accordance with my invention.

Figure 2 is a connection diagram of the same transformer. 1

Figure 3 is a circuit diagram similar to Figure 1 of an alternateconnection for obtaining the desired phase relations.

Figure 4 is a circuit diagram of the internal connections of the tubewith which my invention may be used and the connections of said tube tothe transformer.

Figure 5'is a graph explanatory of the operation of my invention.

Figures 6 and 7 are circuit diagrams of the primary and secondary of apair of transformers which may be used with a modification of myinvention using two tubes, while Figures 8 and 9 show a modification ofthe invention shown in Figures 6 and 7.

Referring, now, to Figure 1 which is a conventional circuit diagram ofthe primary andsecondary of the filament transformer connected inaccordance with my invention, numerals I, II and III designate the deltaconnected primary of the transformer. Obviously, of course, the primarymay be connected in a star connection if so desired. The secondary isconnected in; a star arrangement as shown with the neutral point 11. andoutput terminals, a, b; c, d, e and f. The angular phase relationshipbetween the currents from these output terminals is indicated in the"tubes for this modification may be obtained in dashed lines a, b,

*ing

drawings. It will be seen that the phase relationship between terminals11. and b is 30 degrees. Likewise, the phase relationship between 0 andd, and e and f is also 30 degrees. Between terminals b and c, d and e,and f and a, the phase relationship is 90 degrees.

In Figure 2 is shown the connection diagram of the same transformer asschematically shown in Figure 1. The same reference letters are used asin Figure 1.

Figure 3 shows an alternate secondary connection for obtaining therequired phase relationship for the practice of my invention. A deltaconnected secondary is shown which may be substituted for the starconnection shown in Figure 1. The same reference letters for theterminals are used as in Figure 1.

In Figure 4 I have shown a circuit diagram .of the internal connectionsof the tube with which my invention may be used. The filament wiresdenoted by reference letter I are all connected together at a centralneutral point 0. The free ends of each filament wire are led out toterminals 1 to 6, inclusive. These terminals are a connected to theterminals a to ,f, inclusive, of

the transformer as shown in this figure.

In Figure 5 I have shown in a graphical form the relationship betweenthe currents in the six filament wires plotted against time. Thesecurrents are represented by the: solid lines lettered a, b, c, d, eand 1. Since, as explained before, the direction of the current atany'instant of time has no influence on its effect in the tube d, e andf are drawn in a reversed position to indicate the negative halves ofthe filament currents. Thus, the solid and dashed lines above the zeroline indicate the effective currents as regards their tendency toproduce modulation. It will be noted from an inspection of this figurethat all modulation frequencies below the twelfth harmonic, that is, 720cycles, tend to be cancelled.

In one modification of my invention I may use two tubes or two sets oftubes in one amplifier circuit with a pair of filament transformers soconnected that the phase relationship of the currents in one tube or setof tubes is offset 15 degrees from that in the other tube or set oftubes. This tends to cancel the twelfth harmonic leavonly thetwenty-fourth harmonic (1440 cycles) and its multiples to effect theresultant output. This 15 degree phase relation may be obtained with thefilament transformer connected to one tube or set of tubes, as shownschematically in Figure 6, and the other connected as in Figure '7. Thesame reference letters appear in these figures as in Figure 1, however,subscripts 1 and 2 have been added to clearly indicate that thetransformer in Figure 6 is connected to one tube or set of tubes and thetransformer in Figure 7 to the other tube or tubes.

The desired 15 degree phase relationship between the filament current inthe two sets of another way as shown in Figures 8 and 9. In themodification, as shown in these figures, the advantage is obtained thattwo identical transformers may be used, the only change being in theexternal connection of the transformer windings. This is apparent fromFigures 8 and 9 where the angular relationships are clearly shown.

While I have shown and described insome detail several modifications ofmy invention, it is to be clearly understood that my invention is notlimited thereto but that modifications within the scope of my inventionmay be made.

I claim:

1. In combination, a vacuum tube having a polyphase filament with sixlegs connected in a star configuration about a common neutral point,each leg having an-external connection, a source of three phase power,means for deriving the first, second, fifth, sixth, ninth and tenthphases of a twelve phase polyphase current from said source of threephase power and means for supplying each of said phases to alternateter- -minals of said filament.

2. In combination, a vacuum tube having a polyphase filament with sixlegs connected in a star configuration about a common neutral point,means for supplying alternating current to each leg of the saidfilament, the phase relationship between the currents in each of five ofsaid legs to the sixth being substantially 30, 120, 150, 240 and 270degrees, respectively.

3. In combination, a pair of vacuum tubes each having a polyphasefilament with six legs connected in a star configuration about a commonneutral point, separate means for supplying alternating current to thefilaments of each of said tubes, the phase relationship between thecurrents in each of five of said legs to the sixth of each tube beingsubstantially 30, 120, 150, 240 and 2'70 degrees and the respectivephases of the current suppliedto one tube of the pair being advancedsubstantially 15 degrees from that of the other tube.

1. In combination, a pair of vacuum tubes each having a polyphasefilament with six legs connected in a star configuration about a commonneutral point, separate means for supplying alternating current to thefilaments of each of said tubes, the phase relationship between thecurrent in each of five of said legs to the sixth of each tubebeingsubstantially 30, 120, 150, 240 and v2'70 degrees and the respectivephases of the current supplied to one tube of the pair being advanced anodd multiple of 15 degrees from that of the other tube.

5. In combination, a vacuum tube having a polyphase filament with sixlegs connected in a star configuration about a common neutral point andeach leg having an external terminal, a source of alternating currentpower, a polyphase transformer having its primary connected to saidsource of power and a plurality of secondaries, connections from eachpair of alternate terminals of said filament to a secondary winding ofsaid transformer, the connections being so arranged as to impresspolyphase voltages on the filament legs with phase relationships ofsubstantially 30 degrees between each of three pairs of legs and 120degrees between each of these pairs and the other pairs.

6. In combination, a pair of vacuum tubes each having a polyphasefilament with six legs connected in a star configuration about a commonneutral point and each leg having an external terminal, a source ofalternatingcurrent power and a pair of polyphase transformers, eachtransformer having its primary connected to said source of power andeach transformer having a plurality of secondaries, connections fromeach pair of alternate terminals of the filament of each of saidtubes toa secondary of its respective transformer, the connections being soarranged as, to impress polyphase voltages on the filament legs with aphase relationship of substantially 30 degrees between each of threepairs of legs and 120 degrees between each of these pairs and the otherpairs of legs, the respective phases of voltages supplied to one tube ofthe pair being advanced substantially 15 degrees from that of the othertube.

7. In combination, a pair of vacuum tubes each having a polyphasefilament with six legs connected in a star configuration about a commonneutral point and each leg having an external terminal, a source ofalternating current power and a pair of polyphase transformers, eachtransformer having its primary connected to said source of power andeach transformer having a plurality of secondaries, connections fromeach pair of alternate terminals of the filament of each of said tubesto a secondary of its respective transformer, the connections being soarranged as to impress polyphase voltages on the filament legs with aphase relationship of substantially 30 degrees between each of threepairs of legs and 120 degrees between each of these pairs and the otherpairs of legs, the respective phases of voltages supplied to one tube ofthe pair being advanced an odd multiple of 15 degrees from that of theother tube.

8. In combination, a pair of groups of vacuum tubes each tube having apolyphase filament with six legs connected in a star configuration abouta common neutral point, separate means for supplying alternating currentto the filaments of each of said groups, the phase relationship betweenthe currents in each of five of said legs to the sixth of each groupbeing substantially 30, 120, 150, 240 and 270 degrees and the respectivephases of the current supplied to one group of tubes being advancedsubstantially 15 degrees from that of I the other group.

the current supplied to one group of tubes being advanced an oddmultiple of 15 degrees from that of the. other group.

10. In combination, a pair of groups of vacuum tubes each tube having apolyphase filament with six legs connected in a star configuration abouta common neutral point and each leg having an external terminal, asource of alternating current power and a pair of polyphasetransformers, one transformer for each group of tubes, each transformerhaving its primary connected to said source of power and eachtransformer having a plurality of secondaries, connections from eachpair of alternate terminals of the filaments of one of said groups asecondary of its respective transformer, the connections being soarranged as to impress polyphase voltages on the filament legs with aphase relationship of substantially 30 degrees between each of threepairs of legs and 126 degrees between each of these pairs of legs andthe other pairs of each tube, and the respective phases of voltagessupplied to one group of tubes being advanced substantially 15 degreesfrom that of the other group.

11. In combination, a pair of groups of vacuum tubes each tube having apolyphase filament with six legs connected in a star configuration abouta common neutral point and each leg having an external terminal, asource of alternating 'cur.

rent power and a pair of polyphase transformers, one transformer foreach group of tubes, each transformer having its primary connected tosaid source of power and each transformer having a plurality ofsecondaries, connections from each pair of alternate terminals of thefilaments of one of said groups to a secondary of its respectivetransformer, the connections being so arranged as to impress polyphasevoltages on the filament legs with a phase relationship of substantially30 degrees between each of three pairs of legs and 120 degrees betweeneach of these pairs of legs, and the other pairs of each tube, and therespective phasesof voltages supplied to one group of tubes beingadvanced an odd multiple of 15 degrees from that of the other group.

JAMES LESLIE FINCH.

